fix: forks should exit

src/midi.c

@@ -1,6 +1,5 @@
-#include <GLFW/glfw3.h>
 #include <alsa/asoundlib.h>
-#include <bsd/string.h>
+#include <stdlib.h>
 
 #include "types.h"
 
@@ -61,5 +60,5 @@ bool midi_background_listen(const MidiDevice *device,
 
   log_info("(%s) background acquisition stopped by main thread (pid: %d)",
            device->name, pid);
-  return false;
+  exit(EXIT_SUCCESS);
 }